I'd reccomend browsing around on some car audio forums really, thats what I've been doing lately. Im updating the super crappy system in my 84, replaced the HU with a 200 watt nob style one so I didnt have to cut the dash. Got it from a company called custom autosounds, they sell on ebay and elsewhere. Great product if you dont want all the bling bling looking HU and cutting up our dash. On the case of speakers, Id have to back up what the previous poster said about infinity. I bought some 6x9 kappas to put in the rear hatch, 2ohm speakers, should kick ass. On the case of subs, check out a company called Elemental Designs, they make freaking awesome subs for really really good prices.
But I say again, check out a car audio forum, read that, youll find out that 90% of the names you know for subs and speakers are crap.
Edit: My setup will soon beeee....
2
Infinity Kappa 6x9
2 3.5 inch speakers for the dash of unknown company (havent decided yet)
1
75 watt x4 Audiobahn amp
and eventually, one, and maybe two if i choose to,
Elemental Designs SQ10 to go under my driver and maybe passenger seats in .3 cubic foot sealed boxes.